You can point it out to your child as one of several lessons - some people have very bad memories. Some people see things in a very different way than do we. And some people actually will look past the truth even though they are adults and will lie to protect their position. If a US President will do this - and both President Bush and President Clinton were caught in lies - is it any wonder a classroom teacher does the same?
You can use it as a lesson to show that adults are also afraid for themselves and for their position. Is that how we should be? Is that how we must be? Do we live in a society that accepts mistakes and helps us to learn from our mistakes or do we live in a society that emphasized blaming those who are at fault?

My kid heard his teacher lie testifying against him while defending her posision because she was supposed to do something that she did not, and she lied to the officials to ,probably, keep her job. It was heard to take for my 12 year old, but what can we do? The teacher is still at the school without any remorse or hard feelings about what she'd done, and we left the school to another school where they really care about my kid. What is the lesson then? Like everywhere in our society, you are not a criminal until you're caught, so, this situation has to be accepted when you're out of luck to prove the truth.

Yes, there were other children, but it seems wrong to bring in the other kids into the situation. I like your suggestion and I have decided that would be the best plan of action. If anything, I think it points out to my child the importance of telling the truth. Thanks for some great advise! :-)

Without knowing the specifics, the best you can hope for in a situation like this is turning it into a positive learning experience for your child. Under these circumstances, I'd focus less on "proving" I was right and more on removing my child from this teacher's influence. If it's just a case of your word, or your child's word, against the teacher and the principal chooses to believe the teacher there is little you can do except to try to minimize the negative effects the situation will have on your child.

Could you provide some additional information in order to properly answer your first question? Were there other students or other person's present that witnessed the teacher lying? What were the circumstances surrounding what happened?

You asked, "How do you teach your child that lying is wrong when people in high profile positions lie?" You use it as a further opportunity to teach your child. You tell them the truth -- sometimes people lie. Sometime people in authority lie. Just because they do, doesn't make it right. You teach them that your family tries to hold to a higher standard of telling the truth. In the end, its about being able to hold a good conscience and being able to hold your head up high. Its about having character. Its about being comfortable with who you are and your word meaning something. How much respect do you have for the person who you know to have a history of lying? What kind of credibility do they have? Then you could talk about what kind of credibility you want your family to have. No matter what anyone thinks or says, the truth is the truth. It stands on its own merit.